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Administrative Tasks

Introduction

Administrative tasks are responsibilities managed by system administrators (sysadmins). Sysadmins are IT professionals who ensure an organization's computer systems function efficiently and meet operational needs. Their duties include supporting, troubleshooting, and maintaining computer servers and networks.

In this section, we will discuss:

  1. Managing user and group accounts and related system files.
  2. Automating system administrative tasks by scheduling jobs.
  3. Localization and internationalization.

Managing User and Group Accounts

Linux provides robust tools for managing user and group accounts, which are essential for system security and resource allocation.

User Accounts

1. Adding Users
Use the useradd command to create new users. 

useradd username # Creates a user with no home directory

Common Flags for useradd

  • -m: Creates a home directory for the user.
  • -d: Specifies a custom home directory.
  • -c: Adds a comment (e.g., user description).
  • -g: Assigns the user to a group.
  • -s: Specifies the login shell.

Examples: 

useradd -m username 
useradd -d /path/to/home username 
useradd -c "Comment about the user" username 
useradd -g groupname username 
useradd -s /path/to/shell username

2. Managing Users

  • Change Password: Use passwd.

sh passwd username passwd -e username # Immediately expires a user's password

  • Modify User Attributes: Use usermod.

sh usermod -l new_username old_username # Change username usermod -c "New comment" username # Modify comment usermod -g groupname username # Change primary group usermod -d /path/to/home username # Change home directory

  • Display User Information: Use id.

sh id username

  • List User Groups: Use groups.

sh groups username

  • Delete a User: Use userdel.

sh userdel username

  • Manage Password Aging: Use chage.

sh chage -l username # Show password aging information chage -m 14 -M 90 -W 7 username # Set minimum (14 days), maximum (90 days), and warning period (7 days) chage -E year-month-day username # Set expiration date

3. Filter System Databases
Use getent to retrieve information from system databases. 

getent passwd username # Retrieve user password entry
getent group groupname # Retrieve group information

Group Accounts

1. Creating Groups
Use groupadd to create a new group. 

groupadd groupname

2. Managing Groups

  • Modify Group Attributes: Use groupmod.

sh groupmod -n new_group_name groupname

  • Delete a Group: Use groupdel.

sh groupdel groupname

  • /etc/passwd: Stores user account information (Username, Password, UID, GID, Comment, Home Directory, Shell).
  • /etc/shadow: Stores encrypted user passwords and password aging details.
  • /etc/group: Stores group information (Group Name, Password, GID, Member List).
  • /etc/gshadow: Stores encrypted group passwords and group administrators.
  • /etc/skel: Template directory copied when creating new users.
  • /etc/login.defs: Contains system-wide defaults for user account management (e.g., password aging, UID/GID ranges).

Permissions and Ownership

  • Change Ownership: Use chown.

sh chown username:groupname filename

  • Change Group Ownership: Use chgrp.

sh chgrp groupname filename

  • Change File Permissions: Use chmod.

sh chmod 755 filename # Owner: read/write/execute, Group: read/execute, Others: read/execute

Security Best Practices

  1. Strong Passwords: Enforce complexity policies.
  2. Limited Permissions: Grant only necessary permissions to users.
  3. Account Review: Identify and disable unused accounts.
  4. Password Rotation: Require users to change passwords regularly.
  5. System Updates: Patch vulnerabilities promptly.

Commands Comparison

1. passwd and chage

passwd Command chage Command Description
passwd -n chage -m Set minimum password lifetime.
passwd -x chage -M Set maximum password lifetime.
passwd -w chage -W Set warning period before password expires.
passwd -i chage -I Set inactivity period after password expiration.
passwd -S chage -l Show password aging information.

2. passwd and usermod

passwd Command usermod Command Description
passwd -l usermod -L Lock a user account.
passwd -u usermod -U Unlock a user account.

3. useradd and usermod

Option usermod useradd Description
-e Reset expiration date Set expiration date Manage account expiration.
-s Change login shell Set login shell Specify user shell.
-c Modify comment Create user with comment Add or update user description.
-d Change home directory Set home directory Manage user home directory.
-g Change primary group Add primary group Assign primary group.
-G, -aG Add to secondary group Add to secondary group Manage secondary group membership.

Additional Resources

  1. Linux Documentation: Refer to the official Linux man pages for detailed command usage (man useradd, man usermod, etc.).
  2. Security Guides: Explore security best practices from resources like the CIS Benchmarks.
  3. Automation Tools: Learn about scripting and automation with tools like cron and Ansible.
  4. Online Courses: Platforms like Linux Academy and Coursera offer in-depth Linux administration courses.